Researchers examined five years of data from 1,200 married American men and women, aged 57 to 85. People with spouses who were overly critical or demanding were more likely to develop heart disease than those with supportive mates, the researchers from Michigan State University said.

They also found that a bad marriage's harmful impact on heart health increased with age. This may be because marriage-related stress might stimulate more -- and more intense -- cardiovascular responses due to declines in immune function and increasing frailty as people age, the researchers speculated.

Women were more likely suffer poor heart health due to a bad marriage. One possible explanation: Women tend to internalize negative feelings, making them more likely to develop depression and heart problems, according to lead investigator Hui Liu, an associate professor of sociology.

The researchers also found that heart disease seems to lead to a decline in marriage quality for women, but not men. This finding is consistent with the widely held belief that wives are more likely to provide support and care to sick husbands, while husbands are less likely to do so for wives, the study authors said.

"In this way, a wife's poor health may affect how she assesses her marital quality, but a husband's poor health doesn't hurt his view of marriage," Liu explained in a university news release.

Liu added that the findings, published online Nov. 19 in the Journal of Health and Social Behavior, demonstrate the need for marriage counseling and support for older couples.

"Marriage counseling is focused largely on younger couples. But these results show that marital quality is just as important at older ages, even when the couple has been married 40 or 50 years," she said.

The study was funded by the U.S. National Institute on Aging, part of the National Institutes of Health.